Latency measurements on the ALBA Electron units Olmos 2nd Libera Users Meeting 3rd - 4th April 2008

2nd Libera Users Meeting Latency Measurements Latency as Libera response time: “the time from the beginning of the step response up to the moment when the 90 % of the stable state output is reached” Three different setups were analyzed to measure and compare the latency First two setups were proposed by I-Tech (maybe the first by I-Tech and the second by some of you) The last one includes a variation from I-Tech proposals Latency basically depends on the FA processing, that for ALBA Electron is … 1.1153MHz Dec = 112 9.96 kHz Dec = 2 SW Dec = 84 Dec = 56 ~1.6kHz ~3.3kHz LPF -3dB / 2kHz 2nd Libera Users Meeting A. Olmos

2nd Libera Users Meeting FA data counter Based on the analysis and comparison of FA and Turn-by-Turn samples Target is to create a step change on any of the Libera inputs and measure how long does it take to propagate to the output PROCEDURE Time-stamp the TbT sample at the trigger (when step function starts) Look for that sample in the FA data stream Counter_Value = MOD(MT_time_stamp/112 , 2^16) Measure the latency as the time that it takes from that sample until 90% of the final output step level 2nd Libera Users Meeting A. Olmos

2nd Libera Users Meeting FA data counter 2nd Libera Users Meeting A. Olmos

2nd Libera Users Meeting FA data counter FA Voltage C ~280µs FA Voltage C ~420µs This latency measurement setup seems to be not very precise because of its wide range of latency results and poor resolution level (100µs between FA samples) 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (I) 2nd Libera Users Meeting Based on the analysis of the interlock signal generated by the Libera PROCEDURE Interlock signal is obtained from the FA data stream A steep change in the beam position out of a determined threshold will trigger the interlock Latency is measured as the time that Libera takes to trigger the interlock due to a position change out of threshold There’re two scenarios: Corrected and Non-Corrected position offsets 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (I) Non-Corrected position offset Non Gated (Int OFF) Non Gated (Int OFF) Gated (Int ON) 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (I) Non-Corrected position offset C Libera input signal 208µs 97µs Interlock output Xoffset=690µm Zoffset=784µm One FA sample 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (I) Corrected position offset 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (I) Corrected position offset 193µs 314µs 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (II) 2nd Libera Users Meeting Simpler: there’s no need of compensation attenuators Scope triggered with the gate control signal Setting the scope in persistence mode allows “automatic” max/min latency measurements for a determined interlock threshold Again two scenarios: Corrected and Non-Corrected position offsets 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (II) Non-Corrected position offset Non Gated (Int OFF) Gated (Int ON) 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (II) Non-Corrected position offset Gate control signal Interlock output 152µs Xoffset=174µm Zoffset=220µm 252µs 2nd Libera Users Meeting A. Olmos

By Measuring Interlock Signal (II) Corrected position offset 173µs 268µs 2nd Libera Users Meeting A. Olmos

Summarizing … Which setup should we trust? I-Tech reports Comparable with our MIN results for very off-centered beam DIAMOND Brilliance unit Non-Corrected offset ~300µm Xoffset=690µm Zoffset=784µm What’s different in ALBA Electron unit? -CIC filter contribution -Two Notch filters instead of only one  negligible assuming Notch contribution ~10µs Which setup should we trust? Have you measured “your latency”? -Two Notch filters instead of only one  negligible assuming Notch contribution ~10µs 2nd Libera Users Meeting A. Olmos

Beam orbit control estimation 2nd Libera Users Meeting Summarizing … Beam orbit control estimation Fast orbit feedback loop (Beam dynamics / Controls calculations) fH=235 Hz fV=1550 Hz - ALBA sextupoles have extra coils to provide H/V beam correction - Eddy currents reduce the effect of the magnetic field at high frequencies The overall latency of the control loop is 500-600µs 350-450µs on Libera electronics (very worst case) ~50µs distribution of data around the network ~100µs for DMA transfer + correction calculation + writing into power converters Vacuum chamber cutoff fH=235 Hz and fV=1550 Hz  LIMITING FACTOR Beam orbit control will damp oscillations up to 100Hz Vacuum chamber cutoff fH=235 Hz and fV=1550 Hz  LIMITING FACTOR Beam orbit control will damp oscillations up to 100Hz 2nd Libera Users Meeting A. Olmos